Jarosław Kaczyński, (born June 18, 1949, Warsaw, Pol.), Polish politician who served as prime minister of Poland (2006–07).

Jarosław and his identical twin, Lech, first came to the attention of the Polish public as child actors in the popular film Those Two Who Would Steal the Moon (1962). They were educated at Warsaw University, and both later earned law degrees. Their staunch anticommunist orientation was reflected in their activism as students in the 1970s. After a short time working in education, the brothers had by the early 1980s become active in Solidarity, the trade union movement headed by Lech Wałęsa. In 1989–90 Jarosław edited the movement’s newspaper, and, with Solidarity’s rise to power in 1989, he began an active career in government. In 1990 he and his brother founded the Centre Agreement (Porozumienie Centrum) party, which Jarosław headed until 1998. Both Kaczyńskis were elected to the Sejm, the lower house of the Polish legislature, and were appointed to a number of positions of responsibility. The pair had a falling out with Wałęsa in 1993. In 2001 they formed the Law and Justice (Prawo i Sprawiedliwość; PiS) party, which Lech headed from its inception until 2003, when Jarosław took over.

The PiS won a plurality of votes in elections held in 2005 and formed a governing coalition with the Self-Defense Party and the League of Polish Families. It was widely expected that Jarosław would become prime minister, but he declined the post, indicating that he did not want to hinder his brother’s campaign for the presidency. Lech won the presidency in a runoff in October 2005. Though Lech had initially promised not to nominate his brother for the position of prime minister, he did just that less than a year after he took office, and Jarosław became prime minister in July 2006.

The leadership styles of the Kaczyńskis were unorthodox. Strongly nationalistic, they often took an aggressive approach to foreign policy—including hostility toward the policies of the European Union (EU)—and they sharply criticized Poland’s historical enemies, Germany and Russia. Devout Roman Catholics and staunch social conservatives, they adopted a hard line against the widespread corruption present in Polish politics. While advocating a stronger central government and a more comprehensive economic safety net, the Kaczyńskis also endorsed populist objectives such as cutting taxes. Their critics, however, saw their nationalism as excessive. Despite holding vastly similar political viewpoints, the two were markedly different in their governing style. Lech was a more divisive, vituperative character, capable of drawing intense criticism with his candid statements. Jarosław was considered more reserved and shrewdly diplomatic.

The strife-ridden coalition headed by the PiS collapsed in August 2007 amid scandals and the very public display of division by members of Lech’s cabinet. Early elections were called, and the PiS failed to garner a plurality of the votes. The Civic Platform party won a plurality and established a governing coalition, and Jarosław was forced to step down from the position of prime minister in November. Like most Poles, he was devastated by the news on April 10, 2010, that his brother had been killed in a plane crash en route to a commemorative ceremony for the World War II–era Katyn Massacre. In the special election held in June to replace his brother, Jarosław surprised many observers by finishing a relatively close second to interim president Bronisław Komorowski of the Civic Platform party in a crowded field of candidates. Because neither of the top vote getters captured at least 50 percent of the vote, a runoff election between them was held in July, but Jarosław narrowly lost that contest as well.